C++ std::list::rbegin

The std::list::rbegin function returns a reverse iterator pointing to the last element of a std::list. This allows traversal of the list in reverse order, starting from the last element and moving toward the first element. If the list is empty, the returned reverse iterator is equal to rend().

Syntax of std::list::rbegin

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reverse_iterator rbegin() noexcept;
const_reverse_iterator rbegin() const noexcept;

Parameters

The std::list::rbegin function does not take any parameters.

Return Value

Returns a reverse iterator (or a constant reverse iterator for const lists) pointing to the last element of the list. If the list is empty, the returned reverse iterator is equal to rend().

Exceptions

The std::list::rbegin function does not throw exceptions as it is marked noexcept. However, dereferencing the reverse iterator returned by rbegin() when the list is empty results in undefined behavior. It is recommended to check if the list is empty before accessing elements.

Examples for std::list::rbegin

Example 1: Traversing a List in Reverse Using std::list::rbegin

This example demonstrates iterating through the elements of a std::list in reverse order using rbegin() and rend():

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#include <iostream>
#include <list>

int main() {
    std::list<int> myList = {10, 20, 30, 40, 50};

    std::cout << "List elements in reverse: ";
    for (auto it = myList.rbegin(); it != myList.rend(); ++it) {
        std::cout << *it << " ";
    }
    std::cout << std::endl;

    return 0;
}

Explanation:

  1. Define a list: A std::list named myList is initialized with elements {10, 20, 30, 40, 50}.
  2. Use reverse iterators: The rbegin() function provides a reverse iterator pointing to the last element, and rend() provides a reverse iterator one before the first element.
  3. Iterate through the list: The for loop iterates from rbegin() to rend(), accessing and printing each element using the dereference operator (*it).

Output:

List elements in reverse: 50 40 30 20 10

Example 2: Modifying Elements Using std::list::rbegin

This example demonstrates how to modify elements of a std::list in reverse order using rbegin():

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#include <iostream>
#include <list>

int main() {
    std::list<int> myList = {1, 2, 3, 4, 5};

    auto it = myList.rbegin(); // Get a reverse iterator to the last element
    *it = 10; // Modify the last element

    std::cout << "Modified list: ";
    for (const auto& elem : myList) {
        std::cout << elem << " ";
    }
    std::cout << std::endl;

    return 0;
}

Explanation:

  1. Define a list: A std::list named myList is initialized with elements {1, 2, 3, 4, 5}.
  2. Get a reverse iterator: The rbegin() function provides a reverse iterator pointing to the last element.
  3. Modify the last element: The value of the last element is updated to 10 using the reverse iterator.
  4. Print the modified list: The updated list is printed using a range-based for loop.

Output:

Modified list: 1 2 3 4 10